Most of the pixels seem to be consistent with a \(\beta \)  of \(\simeq 1.5\) , as suggested by [1]}. The latter use low-resolution Planck images to constrain \(\beta \) , which amounts to \(\beta \simeq 1.6\)  in the Orion Nebula complex. The median of all pixels in our SED fit is \(\beta \)  of \(\simeq 1.2\) , but when including only pixels with \(\tau _{160}>5\times 10^{-4}\) , which comprise most of the visible structure, the median shifts to \(\beta \)  of \(\simeq 1.4\) . The peak values, around which the \(\beta \)  values are clustered, is \(\beta \simeq 1.6\) . Standard models, however, suggest \(\beta \simeq 2\)  [2]}. The study of [3]} suggests varying \(\beta \)  according to the environment (radiation field). We note that \(\beta \)  can be affected by the presence of an additional warm dust population in the hot gas and we determine low \(\beta \)  in the EON cavity. \(\beta \)  may vary with the grain composition, grain-size distribution, and with the presence of ices on the grains [4]}, [5]}. Extragalactic studies show systematic variations of \(\beta \)  with galactocentric radius, which may be linked to metallicity gradients [6]}, [7]}.
